1. Field of the Invention
This invention is directed to improved compositions containing zinc nitrate and certain plant food nitrogen in aqueous solutions, as a concentrate and as a foliar spray for application on various crops. More particularly, the present invention relates to a storage-stable foliar composition comprised of a synergistic combination of zinc nitrate, ammonium nitrate and up to about 6%, by weight, of urea, in aqueous solution which composition not only exhibits agronomical effectiveness, but also is stable for long term storage under normal ambient conditions.
2. Description of the Prior Art
Zinc deficiency in the soil has been known for years to be a common cause of poor plant growth. It is known from U.S. Pat. No. 3,130,034 that certain zinc deficiencies may be overcome by the incorporation of zinc sulfate in aqueous ammonia to provide solutions having desirable salt out temperatures. This patent points out that the addition of zinc salts to solid fertilizers, such as super phosphate, ammonium nitrate, potassium chloride and the like, is generally not satisfactory since zinc salts render the solid fertilizers hygroscopic, and hence, difficult to store and handle and that the application of zinc in the soil as an aqueous solution is preferable to its application in solid form, because of the ease which liquids can be stored, handled and applied to the soil. For such use, however, it is essential that the aqueous solutions be non-corrosive to permit the use of mild steel equipment and to maintain a high concentration of plant nutrients to permit economical shipment of the fertilizer and to avoid the necessity of repeated applications during the growing season. The concentration of such solutions however, is generally limited by the minimum temperature expected to be encountered in storage or handling of the solution. Unfortunately, aqueous solutions of zinc salts, such as zinc sulfate, are corrosive to mild steel and form relatively large quantities of scale and rust, the most serious problem encountered with zinc salts is their limited solubility, especially in aqueous solutions of ammonium salts to permit their incorporation in these conventional liquid fertilizers.
U.S. Pat. No. 3,620,708 recognizes that while it is possible to obtain practical amounts of zinc oxide in solution in certain high analysis liquid fertilizers, it has been found that such solutions are unstable or incompatible, with formation of precipitates, when diluted or blended with other liquid fertilizer ingredients.
U.S. Pat. No. 3,640,698 is concerned with fertilizer compositions comprising fertilizer solutions of water, urea and ferrous sulfate, zinc sulfate or manganese sulfate, which compositions are suitable for correction of nutrient deficiencies in crops and soils; according to this patent, at certain critical pH range, the aforementioned sulfate salts form novel eutectic compositions with the aqueous urea solutions, thereby resulting in nutrient fertilizer solutions.
U.S. Pat. Nos. 3,930,832 and 4,025,330 disclose the use of zinc nitrate in specific aqueous nitrogen solutions as foliar spray compositions, and specifically, the use of a solution of a zinc nitrate, ammonium nitrate and high concentrations of urea, as foliar spray fertilizer compositions. U.S. Pat. No. 4,025,330 further discloses the obtainment of significantly improved agronomical results with the aforesaid compositions as compared with foliar spray compositions of zinc sulfate, ammonium nitrate and urea, and U.S. Pat. No. 3,930,832 discloses an improved composition as compared with that of U.S. Pat. No. 4,025,330, in requiring the incorporation of an effective amount of a thiosulfate compound as a corrosion inhibitor to carbon steel. However, as is evident from the disclosures of both U.S. Pat. No. 3,930,832 and U.S. Pat. No. 4,025,330, the urea and ammonium nitrate are incorporated in the foliar spray compositions as a fertilizer solution because of the availability of such solutions as commercial fertilizers, and hence, these fertilizer compositions contain on a weight basis, at least about 14% of urea and generally, at least about 20%, by weight, of urea.